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Your gut is home to trillions of microorganisms that help digest food, support immunity and produce chemicals that can affect the body. In recent years, scientists have become interested in the gut-brain axis, the two-way communication system that links the digestive system and the brain. This has eventually raised questions whether the bacteria living inside our gut could influence mood, emotions and even behaviour. A new study has taken that idea into an unusual area: psychopathic personality traits. Researchers found that certain gut and oral bacteria were associated with higher scores for psychopathic traits. However, this does not mean that gut bacteria make someone a psychopath.
The research, published in Translational Psychiatry, looked at 200 adults who completed questionnaires measuring psychopathic traits, empathy and anxiety. Researchers also studied samples of stool, saliva and blood to examine the participants' microbes and metabolic substances. They found differences involving several bacterial species and some metabolites among people with stronger psychopathic traits. The findings are preliminary but could help scientists understand whether biological processes outside the brain are connected with personality and behaviour. It is also important to note that the study was observational, and the researchers could only identify an association.
What Is Psychopathy?
Psychopathy is a personality condition that's linked to traits such as emotional detachment, reduced empathy, impulsivity and antisocial tendencies. It is important to understand that having some psychopathic traits does not automatically mean that a person is violent or criminal.
The researchers in this study were interested in subclinical psychopathic traits, meaning traits that can exist to different degrees in the general population rather than necessarily representing a clinical diagnosis. Their goal was to investigate whether the composition of gut and mouth bacteria was linked with these personality characteristics.
The researchers in the paper wrote, "We hypothesized that the composition of the gut and oral microbiota may be associated with subclinical psychopathic personality traits."
What Did The Researchers Find?
The scientists analysed the gut and oral microbiota of 200 participants and compared them with scores from a psychopathy questionnaire. They found that certain bacterial groups were associated with psychopathic scores. In particular, Allisonella, Prevotella and Cloacibacillus evryensis were strongly associated with higher psychopathy scores. Another bacterium, Treponema vincentii, showed a negative association.
The overall diversity of gut bacteria did not simply differ between people with stronger and weaker psychopathic traits. Instead, the researchers found that the composition of specific microbial communities was associated with psychopathy scores.
The study also identified differences in certain substances produced or influenced by the body's metabolism. Fecal levels of glucose and taurine differed between the groups and were positively associated with psychopathy scores. These findings could provide clues about possible biological pathways connecting the gut and the brain.
How Could Gut Bacteria Affect Behaviour?
The gut and brain communicate through several pathways, including the nervous system, immune system and chemicals produced during metabolism. Gut bacteria can influence some of these processes.
For example, certain bacteria can produce or modify molecules that affect inflammation and brain function. The researchers pointed to possible connections involving inflammation and metabolic changes. Allisonella has previously been linked to inflammatory processes, while Prevotella has been linked in earlier research with differences in brain regions involved in emotional and sensory processing. However, these earlier associations do not prove that either bacterium causes psychopathic traits.
This is where the idea of the gut-brain axis becomes important. Changes in the gut microbiome could potentially influence brain processes, but the brain and behaviour can also influence the gut. Stress, hormones, diet, sleep and lifestyle can all affect the microorganisms living in the digestive system.
Does This Mean Gut Bacteria Cause Psychopathy?
No, this is probably the most important point about the research. The study was cross-sectional, meaning the researchers looked at the participants at one point rather than following them over many years. Because of this, they could identify relationships but could not determine which came first.
It is possible that certain bacteria influence biological processes connected with personality. But the opposite could also happen: behavioural patterns, eating habits, hormone levels or other factors linked to psychopathic traits could change the gut microbiome. The researchers themselves noted that microbiota-brain communication works in both directions.
"Finally, as findings are correlational, causality cannot be established, especially given the bidirectionality of microbiota-brain communication," the researchers wrote.
"For instance, psychopathy-linked factors, such as eating behaviours and hormonal differences could be responsible for shaping gut microbiota composition," they added.
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